Method for manufacture of dry strength paper containing methylamine-epichlorohydrin polymer

ABSTRACT

A CATIONIC, WATER-SOLUBLE, STORAGE-STABLE, METHYLAMINEEPICHLOROHYDRIN POLYMER IS PREPARED BY REACTING A QUANTITY OF A METHYLAMINE-EPOCHLOROHYDRI-N POLYMER WHICH IS WELL BELOW ITS GEL POIN WITH SUCESIVELY ADDED SMALL AMOUNTS OF EPICHLOROHYDRIN UNTIL THE POLYMER NEARS THE STAGE AT WHICH IT IS AN IRREVERSIBLE GEL, AND THEN REACTING THE POLYMER WITH SUFFICIENT METHYLAMINE TO INACTIVATE SUBSTANTIALLY ALL AMINE REACTIVE EPICHLOROHYDRIN RESIDUES PRESENT. AT LEAST THE LAST OF THE REACTION IS PERFORMED AT A TEMPERATURE AT WHICH A PARTICLE DEPOLYMERIZATION OF THE POLYMER OCCURS.

Oct. 10, 1972 D. E. NAGY METHOD FOR MANUFACTURE OF DRY STRENGTH PAPERCONT 3,697,370 AINING METHYLAMINE-EPIGHLOROHYDRIN POLYMER Original FiledNov. 26, 1968 T P MGR qmwmkwk \w auww was 3st \CRQQmS REACT/0N 7'/ME,HOURS I INVENTOR. DAN/E ELMER NAG) ATTORNEY United States Patent Office3,697,370 Patented Oct. 10, 1972 3,697,370 METHOD FOR MANUFACTURE OF DRYSTRENGTH PAPER CONTAINING METHYL- AMlNE-EPICHLOROHYDRIN POLYMER DanielElmer Nagy, Stamford, Conn., assignor to American Cyauamid Company,Stamford, Conn. Application May 22, 1970, Ser. No. 39,874, which is adivision of application Ser. No. 778,934, Nov. 26, 1968, now Patent No.3,567,659. Divided and this application Dec. 8, 1970, Ser. No. 96,191

Int. Cl. D21h 3/38 US. Cl. 162-164 3 Claims ABSTRACT OF THE DISCLOSURE Acationic, water-soluble, storage-stable, methylamineepichlorohydrinpolymer is prepared by reacting a quantity of amethylaminc-epichlorohydrin polymer which is well below its gel pointwith successively added small amounts of epichlorohydrin until thepolymer nears the stage at which it is an irreversible gel, and thenreacting the polymer with sufiicient methylamine to inactivatesubstantially all amine reactive epichlorohydrin residues present. Atleast the last step of the reaction is performed at a temperature atwhich a particle depolymerization of the polymer occurs.

Water-soluble polymers of higher molecular weight and larger dimensionsare produced by graft polymerizing one or more water-soluble vinylmonomers upon a hydrophilic water-dispersible cationicpoly(hydroxyalkylene) polyamine, which is not necessarily the foregoingpolyamine. The polymers are flocculants for suspended solids in sewageand mine effluent water and dry strength agents for paper.

This is a division of my copending application Ser. No. 39,874, filed onMay 22, 1970, which is a division of my then copending application Ser.No. 778,934, filed on Nov. 26, 1968, now US. Pat. No. 3,567,659.

The present invention relates to hydrophilic, watersoluble orwater-dispersible, cationic, storage-stable methylamine-epichlorohydrincondensation polymers, to water-soluble or water-dispersible cationiccopolymers prepared by a graft polymerization of water-soluble vinylmonomers upon hydrophilic water-dispersible cationic poly(hydroxyalkylene) polyamines (including said methylamine-epichlorohydrinpolymer), to the flocculation of suspended matter in aqueous media bythe use of one or more of the aforesaid polymers, and to paper ofimproved strength prepared by use of one or more of the aforesaidpolymers. The invention includes the processes as well as thecompositions of matter involved.

The manufacture of paper which possesses dry strength alone, or both dryand wet strength, is a specialty of the paper making art, and new resinsfor these purposes are constantly desired.

A major advance in the foregoing art occurred when it was found that thewater-soluble cationic polymer formed by reacting methylamine withepichlorohydrin in one step as disclosed and claimed in copendingapplication Ser. No. 706,592, filed on Feb. 19, 1968 by A. T. Coscia,now US. Pat. No. 3,493,502, possessed the property of flocculatingsuspended solids in aqueous media and thereby increasing the speed withwhich such suspensions could be settled and filtered. This polymer ischemically unstable and sets to a gel unless at low pH.

It has now been discovered that the polymer which is obtained whenmethylamine is reacted with epichlorohydrin in accordance with thecritical limitations hereinafter set forth, possesses in preferredembodiments the following preferred properties;

(1) It is stable indefinitely in aqueous medium at normal storagetemperatures, up to at least F. (2) Each component of the polymer (theunits and the -CH CH(OH)CH hydroxypropylene units) is stronglyhydrophilic so that the polymer is water-soluble when having a molecularweight up to 1,000,000 or more.

(3) It is an active substrate for ceric ion-catalyzed graftpolymerizations, and long vinyl chains can be formed thereon. Graftpolymers produced by this reaction are unusually eifective flocculantsand dry strength agents for paper.

The aforesaid stable methylamine-epichlorohydrin polymer is prepared bya process which comprises several steps.

In the first step, one mol of methylamine is reacted in aqueous alkalinesolution with an amount of epichlorohydrin (0.8-0.9 mol) which is closeto but safely (e.g., about 0.1 to 0.2 mol) short of the amount whichwould produce an irreversible gel. In this step sufiicient time isallowed so that substantially all of the epichlorohydrin reactsbifunctionally with the methylamine. When performed in an open vesselthe mixture is maintained at low temperature to prevent volatilizationof methylamine, after which the temperature is allowed to rise to atemperature at which bifunctional reaction of epichlorohydrin goes tosubstantial completion.

In the second step the polymer is reacted at a pH above 8 with smallamounts of epichlorohydrin (e.g., about 0.05-0.005 mol ofepichlorohydrin per mol of methylamine originally taken) at spaced timeintervals until the polymer has advanced close to the point ofirreversible gelation. A suflicient interval of time (3 to 10 minutes)is allowed to elapse between the addition of each increment ofepichlorohydrin so that each increment of epichlorohydrin reacts almostcompletely bifunctionally before the next increment is added, asevidenced by the viscosity of the solution becoming substantiallyconstant between each addition. It is difi'icult to cause all of theepichlorohydrin to react bifunctionally and hence the polymer in thisstep contains a small amount of aminereactive epichlorohydrin residues.

In the third step the epichlorohydrin substituents attached to thepolymer (and any free epichlorohydrin in the solution) are inactivatedby reaction with a watersoluble primary or secondary amine aspolymerization terminator. The resulting polymer is storage-stable andis then ready for use.

The amine (hereinafter termed amine terminator) also controls the extentof the depolymerization reaction, and if the amount of this amine is toolarge in any instance, the molecular weight of the polymer will be toolow unless the reaction is quenched by cooling or otherwise in advanceof complete reaction of the amine. The amount of amine needed in anyinstance depends upon the number of epichlorohydrin residues in thesolution, the functionality of the amine (whether primary or secondary),and on the number of quaternized nitrogen atoms in the polymer. Asuitable amount of amine is that which is sufiicient to prevent thepolymer from gelling during further heating or on storage. Afteraddition of the amine the polymer solution is maintained at adepolymerization temperature at least until the polymer has becomestoragestable. Further heating may cause additional depolymerization andis within the scope of the process.

The amount of amine terminator needed in any instance for one of thesepurposes cannot be readily calculated, but can be found by laboratorytrial. In our work so far,

1 to 2 mol percent of the amine (based on the number of mols ofepichlorohydrin taken) has been sufficient to prevent gelation andproduce very satisfactory polymers which are storage-stable.

The depth of the decline in viscosity which occurs after attainment ofmaximum viscosity (section B) may be more or less than that shown in thedrawing, depending on the amount of amine terminator added and length oftime the solution is maintained at depolymerization temperaturethereafter. With careful control of the amount of amine added'and theduration of heating, it is possible to inactivate the epichlorohydrinresidues and to terminate the polymerization reaction while the polymersolution is close to the gel point without significant subsequentdecline in viscosity.

In most polymerizations which have a gel endpoint it is common practicevto decrease the temperature of the reaction mixture as the gel point isapproachedso as to retard the rate of reaction when the viscosity isincreasing most rapidly and thus permit the reaction to be safelyterminated close to but short of the gel point. We have discovered,however, that in the reaction of the present invention the gel point canbe safely approached at high temperature, provided that the temperatureis sufficiently high. We have found that safe temperatures lie withinthe range of. 70 C.-100 C.

The reason why temperatures in this range are safe hasnot beenascertained. We have established that heating the polymer at thistemperature in the presence of amine terminator causes adepolymerization reaction which is generally sufficient to preventpassage of the polymer from watch-soluble state into an irreversible gelstate, and to convert any reversible gel which has formed back into,water-soluble polymer state. The nature of the depolymerizationreaction, however, has not been ascertained. From the fact that itcauses a major decrease in viscosity of the polymer, often by 50% ormore, we believe that the depolymerization reaction involves a scissionof carbon-nitrogen quaternary ammonium bonds (-i.e., scission ,of carbonbonds which are attached to quaternary ammonium nitrogen atoms), withconsequent conversion of quaternary atoms to tertiary State anddiminution in the .number of cross-linkages-in the polymer. The speed ofthe depolymerization reaction varies mainly with the pH of the solutionand temperature, the depolymerization being favored by high pH and hightemperatures. Suitable pH values and temperatures can be found bylaboratory trial, employing the methods 'shoWn in the examples below. Asa rule of thumb we have found that at about pH 9 a temperature of about75 C. is satisfactory and that at about pH 8, a temperature of about 95C. is satisfactory.

The depolymerization reaction, as far as we know, is not detrimental tothe elficiency of the polymer as flocculant or as dry strength agent forpaper. Its principal benefit is that. it permits a high molecularweight, watersoluble, storage-stable polymer to be prepared close to itsgel point while greatly decreasing the danger of formation of anirreversible gel, and facilitating the entire operation.

The product of the above-described process is largely composed of unitsof the formula but may contain a small proportion of cross-linkages ofundetermined formulae. The polymer is accordingly most convenientlydescribed in terms of its method of preparation. For convenience it issometimes hereinafter termed a poly(hydroxypropylene) poly(methylamine).

The aforesaid poly(hydroxypropylene) poly(methylamine) and the graftpolymers thereof which are described herein below, in some instancesform clear solutions when dissolved in water. In other instances, theyform colloidal solutions, i.e., solutions which are iridescent oropalescent, resulting from the fact that the macromolecules therein areof colloidal or near-colloidal dimensions and either at or close to theborderline which exists between water-solubility and water-insolubility.For convenience, in the specification and the claims all these polymersare designated as water-dispersible, it being understood that the termincludes water-soluble.

The reaction of the present invention tolerates the presence of otherm-aterials..Thus, up to about 20 mol percent of the methylamine can bereplaced with other water-soluble primary amines, for exampleethylamine, propylamine, ethanolamine, cyclohexylamine, etc. 'withsubstantially the same results, and the resulting polymers are withinthe scope of the present invention.

Suitable water-soluble amines for stopping the reac: tion areethylamine, piperidine, diethylamine, ethanolamine, dimethylamine andmethylamine itself. While secondary amines give better resultsmethylamine gives satisfactory results and because of its prior use inthe process, is preferred.

The effect of the depolymerization reaction is illustrated by thedrawing, which represents a plot of the changes in viscosity (curve 1)and .a plot of the changes in temperature (curve 2) which occur as afunction of time when methylamine and epichlorohydrin are reacted inaccordance with an embodiment of the invention in which theepichlorohydrin is added with about maximum rapidity. Curve 1 is dividedinto sections A-F, as shown by the lettered dotted lines.

In section A, 0.9 mol of epichlorohydrin is added to 1 mol ofmethylamine in a jacketed kettle provided with stirrer and refluxcondenser over two hours. The temperature of the reaction mixture iscontrolled at 25 C. to minimize volatilization of methylamine, but atthe end of the period is allowed to rise to C. At the end of the secondhour, sufficient acid acceptor solution (concentrated sodium hydroxidesolution) is added to maintain the pH at above 8.5 during the remainderof the reaction. During most of this period the viscosity of thereaction mixture remains substantially constant. At the end of theperiod, reaction of the epichlorohydrin is substantially complete.

In section B, epichlorohydrin is added in increments of decreasing size,first of 0.01 mol and then of about 0.005 mol at intervals of about fiveminutes resulting in small stepwise increases in viscosity (shownschematically in drawing). At the end of the period of time covered bythis section the viscosity of the reaction mixture rises almostvertically, and addition of epichlorohydrin is stopped.

At the start of section C, sufficient methylamine is added (1% based onthe weight of the methylamine originally taken) to inactivate theamine-reactive epichlorohydrin substituents present and to inactivateany free (wholly unreacted) epichlorohydrin present, together with aquantity of cold water to slow the rate of viscosity increase. Themixture is heated back to 95 C. The methylamine reacts as reactionterminator, and the depolymerization reaction begins. The methylamine isadded to provide an excess over the minimum needed to inactivate theepichlorohydrin residues. The methylamine does not react immediately,and the viscosity of the solution continues to climb. As a result ,ofthe depolymerization reaction and inactivation of the residualepichlorohydrin the climb stops at a viscosity of about 95 seconds, atwhich point the polymer is close to its gel point. In section Bdepolymerization is the only reaction which occurs, and the viscositydrops rapidly to about 30 seconds and levels off, as shown by theportion of the curve shown by dashes (section F). The solution is cooledto room temperature and is then ready for storage or use.

The solution obtained may be spray dried. The polymer is recovered as afree-flowing powder which dissolves readily in water. The solutionobtained by dissolving the polymer in water possesses substantially allthe properties of the solution prior to being spray dried.

The aforesaid polymer solution, as produced by the process outlinedabove, possesses desirable fiocculating properties and is storage stableeven though containing 20% polymer solids by weight and even though thepolymer is of high molecular weight and close to the gel point. Whenused as a flocculant the polymer solution is advantageously diluted to1%5%l concentration and is uniformly incorporated into the suspension tobe clarified in amount suflicient to cause the suspended particles tocoalesce and precipitate. The proper amount varies from instance toinstance depending chiefly upon the zeta potential of the particles andthe cationic charge of the polymer and is most conveniently found bytrial on a sample of the suspension to be clarified. The polymersolution is effective for the flocculation of the suspended solids insewage, mine effluent water and papermill white water. The pH of thesuspension to be clarified is not critical and may be in the range of4-10.

In the manufacture of paper the polymer is advantageously added to apapermaking furnish having a pH of 5-9, at the fan pump or similarlocation in an effective amount as dry strength agent. About 0.1% basedon the dry weight of the fibers is about the least amount which producesa significant strengthening effect, and more than about 3% on the samebasis does not produce commensurate increases in strength and so thisamount is regarded as the practical maximum. The suspension is formedinto paper in customary manner, and no special drying or other treatmentis necessary. The product is paper composed of cellulose or othernegatively-charged fibers bonded together by an adsorbed content of thpolyamine.

Additionally I have found that valuable water-soluble cationic polymersof very high molecular weight, which may be thermosetting, are producedwhen a water-soluble poly(hydroxyalkylene) polyamine is graftpolymerized by the ceric ion method of Mino !et al. US. Pat. No.2,922,768 with a water-soluble vinyl monomer or mixture of monomers. Ihave found that such graft polymers are thremosetting when thepoly(hydroxyalkylene) polyamine used as the substrate for the graftpolymerization is thermosetting. The polymers produced in this mannerare useful as fiocculants and as agents which improve the strength ofpaper. They are employed in the same manner as heretofore knownpolyamine agents.

The substrate polymers used for the preparation of the graft polymers ofthe present invention contain linkages and it is thought that thepresence of OH substituents in these linkages is the reason why thegraft polymerization reaction proceeds with formation of suchsatisfactory products. The composition of the polymers is illustrated bythe instance where the storage-stable methylamine-epichlorohydrinpolymer of the present invention is the substrate; in that instance thegraft polymer has the theoretical formula:

wherein the Ms represent graft polymerized vinyl chains. It will be seenthat the polymeric vinyl chains are attached to the same carbon atoms towhich the OH substituents are attached.

The vinyl monomers which can be graft copolymerized include vinyl amidessuch as acrylamide, methacrylamide, dimethyl aminoethyl methacrylate,and the like; vinyl acids such as acrylic and methacrylic acid; vinylnitriles such as acrylonitrile, methacrylonitrile and the like, andesters such a methyl acrylate, methyl methacrylate, and mixtures of suchvinyl monomers. Vinyl amides, particularly acrylamide, and mixtures ofacrylamide with one or more of the monomers listed above, are preferablebecause they produce a product which is highly water-soluble, whichpossesses excellent fiocculating properties, and excellent strengtheningproperties for cellulose papermaking fibers. Where the monomers arepresent, it is preferred that acrylamide be at least 75 mol percent ofthe mixture. In every instance where the graft polymer is not subjectedto a solubilization treatment the proportions of watersoluble vinylmonomer in the polymerization mixture is such that the graftpolymerization product is hydrophilic and water-dispersible as at leasta colloid solution.

Acrylonitrile and other vinyl monomers which produce insoluble graftcopolymer products can also be used to form the vinyl substituents ofthe graft copolymers of this invention in which event the graft polymeris subjected to a solubilization treatment. For example, whenacrylonitrile alone is the vinyl monomer to be polymerized, the graftpolymer may be insoluble in water and if insoluble the polymer can besolubilized by hydrolysis of nitrile groups with alkali. Thepoly(hydroxyalkylene)polyamines are highly receptive to graftpolymerization, and it is readily feasible to graft polymerize on thepolyamine substrates a weight of vinyl monomer which is many times theweight thereof. However, when the weight of the grafted monomer is morethan roughly 10 times the weight of the substrate the properties of thesubstrate nucleus tend to become masked and the properties of thepolymer are predominantly those of the grafted vinyl material.

Reciprocally, when the amount of grafted material is less than roughly$5 the weight of the polyamine, the effect of the grafted material inaltering the properties of the polyamine nucleus is not significant, andthis is regarded as the practical minimum. In practice, then, the weightof the grafted vinyl material is between about 5 and 10 times the weightof the polyamine, and we prefer the intermediate range of /2 to 5 timesthe weight of the polyamine.

The ceric ion catalyst is essentially a dilute aqueous acidic solutionof a water-soluble ceric salt. A 0.1 N solution of ceric ammoniumnitrate, ceric sulfate, ceric ammonium sulfate, etc. in 1 N nitric acidis satisfactory. Only a small amount of ceric salt (from 1 to 1() l0-mol per mol of vinyl monomer) is needed and the polymerization proceedsat room temperature even in the presence of free (dissolved) oxygen.Very little homopolymerization occurs, and hence the amount of vinylmonomer which is grafted is usually above of the amount supplied to thereaction mixture.

The poly(hydroxyalkylene)polyamines which are benefited by graftpolymerization according to the present invention are water-soluble,preferably but not necessarily of high molecular weight, and have asubstantial content of hydroxy-alkylene linkages. They may but need notbe thermosetting, and, when thermosetting impart wet strength inaddition to dry strength. Their molecular size may range from the sizeat which they are composed of a few monomeric units to several hundredthousand or more. At least 10 mol percent of the alkylene unitsconnecting the aminonitrogen atoms should contain at least one hydroxylsubstituent each.

Suitable poly(hydroxyalkylene)polyamines of the foregoing descriptioninclude the water-soluble thermosetting polymers prepared by reactingammonia with epichlorohydrin, by reacting a mixture of ammonia and awatersoluble alkylene-polyamine in 1:1 molar ratio with epichlorohydrin,by reacting a 6:1 molar ratio methylamine: ethylenediamine mixture withepichlorohydrin, by reacting methylamine and epichlorohydrin asdisclosed in said copending application; by reacting a 1:1 molar ratiomixture of ammonia and guanidine with epichlorohydrin, and by reactingdiethylenetriamine with epichlorohydrin. Detailed methods for thepreparation of these and other poly-(hydroxyalkylene)polyamines aredisclosed in US. Pats. Nos. 2,585,935 and- 2,595,936, and Coscia US.Pat. No. 3,248,353. Such polymers can be prepared in non-thermosettingstate by inactivating any unreacted epichlorohydrin substituents presentby adding dimethyl amine to the reaction mixture so that thepolymerization process is halted before the polymer has reached the gelstage.

The graft copolymerization reaction using a methylamine-epichlorohydrinresin is carried out at an acid pH, preferably at a pH of about 3 to andin the presence of sulfate ions. The pH of the reaction mass isinitially adjusted to 5 or below before or immediately after addition ofthe catalyst. The pH is preferably maintained below 5 but above 3 duringthe remaining course of the graft polymerization reaction. It has beenfound that if the pH of the reaction mass is permitted to fall below 3,the conversion rate of the copolymerization reaction is significantlylowered.

The graft copolymers of this invention can be of any desired molecularweight so long as they are soluble or dispersible in aqueous medium,within the pH range of 4-10.

The viscosity of solutions of the graft copolymers of this invention canbe reduced by the addition of small amounts of an alcohol, such asisopropanol, methanol, ethylene glycol, or propylene glycol. Theviscosity-reducing agent is added to the reactants as disclosed in theaccompanying examples.

Concentrated solutions of high molecular weight graft copolymersof thisinvention can be, in some instances, quite viscous, and may even takethe form of firm gels. Such gels form mobile aqueous solutions ordispersions when stirredwith several times their weight of water havinga pH in the range of 4-10.

The process for preparing the graft copolymers of the present inventioncan be carried out at temperatures between about C. and 90 C. andpreferably at temperatures between about 25 C. and 55 C. Temperaturessignificantly above 80 C. are preferably avoided because the exothermicreaction may proceed too rapidly at these high temperatures, and lead toslightly less effective polymers.

While this process can be carried out under pressure or partial vacuum,if desired, atmospheric pressure operation has been found mostsatisfactory.

The cationic amine, graft copolymer removal agents can be added to thewaste water system being treated inwidely varying'amounts, depending onthe degree of waste removal desired in the system. The amount of removalagent added canalso vary with the nature of the treatment system, thatis, whether it: is a primary or secondary treatment system, and with thepermissible dwell time in the system.

The cationic copolymer removal agents can be added to the waste watersystem in amounts, from about 0.001 to about 5 percent. by weight of thedispersed solids.

Preferably, concentrations of removal agent in the wastewater systemshould be maintained between about 0.1 and 2 percent by weight of thesuspended solids.

The invention is further illustrated by the examples which follow. Theseexamples are preferred embodiments of the invention and should not beconsidered as limitations thereon.

EXAMPLE 1 The following illustrates a preferred method for thepreparation of the methylamine epichlorohydrin polymer of the presentinvention.

To 100g. of methylamine (3.25 mols) dissolved in 400 g. of water in areaction flask provided with stirrer,

thermometer and reflux condenser is added 260 g. of epichlorohydrin (2.8mols, equivalent to 0.87 mol per mol of amine) over 60 minutes, cooling(by Dry Ice bath) being applied as necessary to keep the temperature ofthe reaction mixture between 25 C.40 C. at the first half of thereaction and at 50 C. C. during the second half of the reaction. 160 g.of 36% aqueous sodium hydroxide solution (1.44 mol) at C. is then addedto the reaction mixture. The reaction mixture is then heated to C. andepichlorohydrin is added in 1 ml. mol) portions and the viscosity of thereaction mixtureis followed by filling a 6 mm. (inside diameter)vertical glass tube with the hot solution and noting the number ofseconds required for the level of the solution to fall 13 inches whenthe bottom of the tube is opened. Results are as follows:

Ml. epichloro- Time hydrin Temp., Viscosity (minutes) 1 added 0.(seconds) 2 1 From start of reaction. 2 Of reaction mixture, by glasstube method.

After 132 minutes, the reaction mixture becomes very viscous and theviscosity continues to rise. There is then added 274 g. of cold watercontaining 0.8 ml. of methylamine as reaction terminator, and thereaction mixture is heated to 94 C. The following viscosity changesoccur:

Temp. Viscosity, Time (minutes) 1 0.) seconds 1 EXAMPLE 2 Thisillustrates the effectiveness of the polymer in Example l as fiocculant.

The apparatus employed consists of a No. 2 Biichner funnel having itsstem connected air-tightly to a volumetric cylinder through'an adapterhaving a side-arm which is connected to a gauged vacuum source. A sheetof No. 2 Whatman filter paper is placed in the funnel over a wiremeshscreen support. For each test, a 300 ml. sample of sewage sludge (4.3%solids) is placed in a 400ml. beaker. A 1% by weight solution in waterof the polymer of Example 1 is measured into a similar beaker. Thesludge is then poured into the polymer solution and the mixture ispoured back and forth between the beakers three times to ensure completemixing. The resulting mixture (a .conditioned" sludge) is then pouredinto the Biichner funnel (the filter paper in the funnel having beenpreviously moistened and applied under vacuum to form a seal). After5-10 seconds (to permit turbulence to" cease) 30" of vacuum is appliedto the funnel and the time required for 100 ml. of filtrate to passthrough the filter is recorded. The test is repeated, the polyamidebeing replaced by a laboratory standard flocculant (flocculant C31 ofthe Dow Chemical Co.) as control.

The filtration rate of the sludge treated with the poly-. mer of thepresent invention is about twice as fast (2.04 times) as that of thecontrol.

9 EXAMPLES 3-6 This series of examples shows the efiect of variations inthe amount of alkali added to the reaction mixture.

The general procedures of Examples 1 and 2 are repeated with variationsas follows.

Example 3: Addition of the sodium hydroxide solution is commenced when34% of the epichlorohydrin has been added and is completed in 1.6 hours.The remaining 66% of the epichlorohydrin is added over two hoursstarting with the addition of the sodium hydroxide solution. Thesolution is then heated to 79 C. After the odor of epichlorohydrin hasdisappeared from the solution, during the next four hours, a total of 27g. of epichlorohydrin is added to the reaction mixture in l g. portions.The viscosity of the solution is allowed to become constant between eachaddition. At the beginning of the four-hour period, the viscosity issuch that one second is required for the solution to descend 13 inchesin the glass tube. At the end of the fourth hour 7 seconds are required,and no more epichlorohydrin is added. The viscosity climbs as follows.

Minutes after last addition of epichlorohydrin Viscosity (seconds) 1 1Of hot solution, by glass tube method.

After 110 minutes the viscosity is increasing rapidly and gelationbegins. At this time 125 ml. of cold water and 3.7 g. of 40% methylamineare added and the reaction mixture is reheated and held at 75 C. After245 minutes gelation is reversed and the viscosity of the solutionfalls, owing to scission of bonds in the polymer molecule and consequentdepolymerization.

After 582 minutes the heating is discontinued. The resulting polymer iscooled and is storage-stable.

Examples 4-6: The general procedure of Example 3 is followed with thefollowing exceptions: (1) different amounts of alkali are used asrecorded in the table below, and (2) the temperature of the reactionmixture is maintained at 90 C. during the incremental addition of 1 g.portions of epichlorohydrin. In Example 6 alone, the alkali is addedconcurrently with the epichlorohydrin from the beginning of thereaction.

The polymers prepared in Examples 3-6 are evaluated as sewagefiocculants according to the procedures outlined in Example 2. Resultsare as follows:

Mols epi- Mols ehloro- Flocculant NaOH hydrin Soln. of efficiency addedreacted 1 pH 1 polymer 3 0. 525 0. 965 8. 65 S1. better.

1 Per mol of methylamine. 3 After addition of epichlorohydrin. I Basedon filtration rate produced by laboratory standard floeculant.

EXAMPLE 7 The following illustrates th storage stability of a solutionof the methylaminc-epichlorohydrin polymer at the solids content atwhich it is normally prepared, at various temperatures and pH values.The samples stored at the 7 temperatures shown and are observed fromtime to time. Results are as follows:

Viscosity C. after 12 mos.

No change. 5 Do.

The results indicated that the polymer is stable indefinitely.

EXAMPLE 8 An aqueous solution corresponding to that prepared in Example1 containing 20%; polymer by weight and having a pH of 6.3 is fed into alaboratory spray drier at the rate of 50 ml. of solution per minuteunder conditions such that the inlet air temperature of the drier is 400F. and the outlet air temperature is 150 F. The size of the sprayedparticles and the duration of the drying are such that the productcontains 5% moisture by weight and flows freely when poured from acontainer.

The product is a free-flowing powder which dissolves rapidly in waterforming an opalescent solution therein. The resulting solution possessessubstantially the same efficiency as flocculant and as dry strengthagent for paper as the parent solution.

EXAMPLE 9 The following illustrates the ease with which the polymer ofthe present invention undergoes graft polymerization with acrylamide toform a polymer of high molecular weight. The ratio of the polymer to theacrylamide is 1:1 by weight.

To 85.6 g. of a 23.6% by weight aqueous solution of the water-soluble,stable cationic polymer of Example 1 having a viscosity of 244centipoises at 25 C. are added consecutively 50 ml. of water, enough 50%H to lower the pH to 4.8, 20 g. of acrylamide, 4 ml. of isopropylalcohol and sufficient water to increase the weight of the solution to188 g.

To this is quickly added with stirring 12 ml. of ceric catalystsolution, prepared by mixing ceric ammonium nitrate and concentratednitric acid in water to yield a solution 0.1 N with respect to ceric ionand 1 N with respect to nitric acid, as disclosed in said Mino et al.patent.

The temperature of the reaction mass rises to 52 C. approximately oneminute after addition of the eerie solution, and the solution reaches ahigh viscosity in the first two minutes.

After standing overnight, the final pH of the reaction mass is about 3.2and the aqueous solution of the graft copolymer product has a viscosityof 70,000 centipoises at the concentration of 20% active solids, whichindicates that the molecular weight of the graft polymer is in excess of1,000,000.

EXAMPLES 10-12 The following shows how the viscosity (and thereforemolecular weight) of the graft copolymer can be controlled by varyingthe amount of alcohol.

The procedure of Example 9 is repeated except that the amount ofisopropyl alcohol added is varied as shown in the table below. Theresults show that the molecular weight of the graft copolymer decreasesas the amount of alcohol increases. The viscosities were determined onthe final solution at-uniform solids content and at 25 C.

Viscosity Ml. iso- (cp.) of propane] polymer Example EXAMPLE 13 Thefollowing illustrates the preparation of a polymer similar to that ofExample 9, except that the weight ratio of the polymers is 3:1.

To 83.5 g. of a 24% solution of a methylamine epichlorohydrin polymerprepared by the method of Example 1 having a viscosity of 500centipoises are added consecutively suflicient 50% sulfuric acid toadjust the pH to 5.4, 60 g. of acrylamide, sufficient water to increasethe weight of'the solution to 400 g., and 24 ml. of the 0.1 N ceric.solution of Example 9 in one portion with stirring. An exothermicreaction occurs, and the solution becomes a firm gel having a final pHof 4.1. Water is added and the gel is stirred slowly. The gel dissolves.The resulting solution is diluted with water to 3% polymer solidscontent by weight and the resulting solution is viscous.

This solution is highly efiicient as a sewage flocculant. In comparativetests, it is found that the optimum amount of the product of thisexample needed for effective sewage solids removal is only 75% of theamount required of a commercial sewage flocculant. Further, water can befiltered through the sludge produced by the graft copolymer of thisexample three times as fast as it can be filtered through the sludgetreated with the commercial flocculant.

EXAMPLE 14 EXAMPLE 15 The procedure of Example 13 is again repeatedexcept that g. of acrylamide is used (1:1 acrylamidezpolymer ratio).After the alkaline hydrolysis, the resinous copolymer product is solublein water but precipitates when the pH is lowered to about 5.0. Theprecipitated resin is redissolved almost completely when excess acid isadded.

EXAMPLE 16 The following illustrates the preparation of a polymeraccording to the present invention wherein the backbone ispolyacrylonitrile.

To 100 g. of a 20% solution of methylamine-epichlorohydrin cationicpolymer. having a viscosity of 504 cp. at.25 C. is added suflicient 50%H 80 to decrease the pH of the solution to 3.9 and sufficient water toproduce a total solution weight of 1300 g. The solution is sparged withnitrogen and 100 g. of acrylonitrile is added, followed by 15.5 ml. ofthe 0.1 N ceric solution of Example 9. Immediately after addition of theeerie solution, the reaction-mixture warms and becomes cloudy andwhitish, and thickens. Afterstanding overnight, the resinous reactionproduct is added slowly to 118 g. of sodium hydroxide in 1 liter ofwater at 95 C. Hydrolysis occurs with formation of carboxyl groups, asshown by theproduct becoming soluble in water. The resulting redsolution becomes colorless and homogenous in about 2 hours. It is heldat C. for a total of six hours. A precipitate forms when the clearhomogenous solution is acidified. H

EXAMPLE 17 The following illustrates the grafting of acrylamide and'methylenebisacrylamide upon a polyamine of the present invention.-

To 432 g. of diethylenetriamine in 161 g. of water at 92 C. is added 430g. of epichlorohydrin over a period of 2.5 hours. The solution becomes.viscous and is diluted with water containing ml. of 10 N sulfuric acidto yield a final solution comprising 1462 g. of amine resin (48.2% ofthe weight of the solution). 41.5 g. is diluted to 20% solids byaddition of water, the pH of the solution is adjusted to 2.5 withsulfuric acid, and 20 g. of acrylamide and 40 ml. of a 0.1% by weightsolution of methylenebisacrylamide are added. To this solution is added5 ml. of the 0.1 N ceric nitrate solution of Example 9, and the solutionsets to a water-soluble gel almost immediately.

The solution is an eflfective flocculant for the solids in sewage.

EXAMPLE 18 The procedure of Example 17 is repeated except that only 20ml. of the 0.1% methylenebisacrylamide solution is used. The resultingcopolymer resin solution thickens but does not gel. The product is aflocculant but is considerably less so than the polymer of Example 17.

EXAMPLE 19 mer results. This polymer is a dry strength agent for paper.

EXAMPLE 20 The procedure of Example 9 is" repeated except that 20 g. ofacrylamide-+1 g. of acrylic acid are substituted for the acrylamide usedto form the vinyl substituent.

The graft copolymer is an effective precipitant for the dispersed solidsin sewage.

EXAMPLE 21 The procedure of Example 9 is followed except that 20 g. ofacrylamide-H g. of dimethylaminoethylmetb' acrylate are substituted forthe acrylamide used to form the vinyl substituent.

The graft copolymer is an efl'ective precipitant for the dispersedsolids in sewage.

EXAMPLE 22 The procedure of Example 10 is followed except that 15 g.methylacrylic acid are substituted for the acrylamide used to form thevinyl substituent.

EXAMPLE 23 The following illustrates how the viscosity of the graftcopolymer products of this invention and therefore the molecular weightof the product is affected by changes in the initial pH of the reactionmixture. The materials used and the procedure followed are essentiallythe same as those of Example 9, above, except that no isopropyl alcoholis used. Results are as follows:

pH during Viscosity polymeriof 5 a zation 1 solution 3 1 Based on pHimmediately alter polymerization. The results show that the molecularweight of the graft polymer falls off sharply when the pH of thereaction mixture is allowed to fall below 4.

1 0! reaction product.

EXAMPLE 24 The cationic amine-containing graft copolymers produced byruns A, D, and G of Example 23 and the parentpoly(hydroxyalkylene)polyamine are evaluated as sewage precipitantsasdescribed in Example 2. The results of these runs show that thereaction products of this invention are highly effective precipitantsfor the dispersed solids in sewage, despite major differences in theirmolecular weight. Results are as follows:

pH during Filtration polymerirate of Polymer zatlon sludge 1 1 Based onfiltration rate (taken as 1) cl sludge treated with laboratory controlflocculant.

The results show that the graft polymer produced at pH 3.1 produced asludge which filtered 8.3 times as fast as the sludge treated with thelaboratory control fiucculant.

EXAMPLE 25 The following illustrates the manufacture of paper ofimproved strength by the use of graft polymers of the present invention.

The polymers are prepared by the method of Example 23, except that thepH values of the solution during the graft polymerization is as shown inthe table.

Viscosity of soln. (cp.)

Polymer Burst H during p graft Vise. 01 Percent Percent Run Numberpolymer 5% soln. polymer Lb. increase 1 None 40. 6

14 The results show that the strength-imparting efficiency of the graftpolymer increases sharply as its molecular weight rises.

EXAMPLE 26 This example illustrates a process for preparing the graftcopolymers of this invention in which the vinyl monomer and the cericcatalyst solution are incrementally added to the solution of thecationic amine-cont-aining polymer to permit convenient regulation ofthe pH and the rate of the exothermic reaction. To 171 g. of the 23.0%solution of methylamine-epichlorohydrin condensate of Example 1 in aflask equipped with sparger, stirrer, thermometer and three droppingfunnels are added 40 ml. of water and the solution is acidified to pH4.05 with 50% aqueous H The resulting solution is sparged with nitrogen.

Into the funnels are respectively placed 40 g. of acrylamide and 60 ml.of water; 24 ml. of the 0.1 ceric catalyst solution of Example 1 and 26ml. of water; and 10 ml. of 10% aqueous NaOH solution. One tenth of theceric catalyst solution and one-tenth of the acrylamide are first addedwhile continuing the nitrogen sparge. After about 10 minutes, 1 ml. ofthe NaOH solution is added and then another one-tenth portion of theacrylamide and ceric are added, followed by another 1 ml. of sodiumhydroxide. This sequence is repeated until all the materials have beenadded.

The amount of alkali added is regulated to keep the pH at 3.4. The finalsolution has a viscosity of 272,000 centipoises at 20% polymer solids,indicative of a polymer having a molecular weight of more than1,000,000. Less viscous solutions can be prepared by the procedure ofthis example by adding small amounts of isopropyl alcohol to thereaction mixture.

The invention in its broader aspects is not limited to the specificdetails shown and described, and departures may be made from suchdetails without departing from the principles of the invention andwithout sacrificing its chief advantages.

I claim:

1. Paper of improved strength composed of negatively charged papermakingfibers having a uniformly absorbed content of a polymer prepared bysubstantially completely reacting in aqueous alkaline solution 1 mol ofa methylamine with epichlorohydrin in sufficient amount between 0.8 and1.2 mol to produce a polymer which is cationic and water-dispersible;reacting said polymer successively, substantially but not completely,with increments of epichlorohydrin each less than about 0.1 mol per molof said methylamine at a pH about 8 until the polymer s close to butshort of the point at which it becomes an lrreversible gel whereby saidpolymer contains a small number of amine-reactive epichlorohydrinresidues; adding to the resulting solution sufficient of a water-solubleprimary or secondary amine to prevent said polymer from gelling duringfurther heating and on storage; and maintaining the resulting solutionat a depolymerization temperature at least until the polymer therein hasbecome storage-stable.

2. Process for the manufacture of paper of improved strength whichcomprises adding an effective amount as dry strengthening agent of apolymer according to claim 1 to an aqueous suspension of cellulosepapermaking fibers having a pH of 5-9, forming the suspension into aweb, and drying the web to form paper.

3. Process for the manufacture of paper which comprises adding aneffective amount as dry strengthening agent of a polymer according toclaim 1 which has been graft polymerized with between A and 10 times itsweight of a water-soluble vinyl monomer in the presence of a ceric graftpolymerization catalyst, to an aqueous suspension of cellulose paper 16making fibers having a pH of 3,314,897 4/1967 Gaertner 162164 X a 59,'forming the suspension into a web, and drying the 3,493,502 2/ 1970Coscia 210-54 web to form paper.

References Cited S LEON BASHORE, Primary Examiner UNITED STATES PATENTS5 F. Frei, Assistant Examiner 2,753,372 7/1956 Lundberg 162164 X3,248,353 4/1966 Coscia 162164 X 3,269,890 8/1966 US. Cl. X.R. Gaertner162164 2-468 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 5&97370 Dated October 10, 1972 Irw fls) Daniel Elmer Nagy Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby-corrected as shown below:

Column 6, line 67, "aminonitrogen" should read amino: nitrogen Column 8,line Y 3 (by Dry I'c'e' should read (by ice- Column 9, line 65, secondtable, second column, "0 900" should readv 0.900 Column 9, line '72,"th" should read the Signed and sealed this 27th day of March 1973.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Office Commissionerof Patents FORM PO-IOSO (IO-6S) U SCOMM-DC GOING-P69 U.S. GOVIIIIMIIITIIINTING OFFICE "I! O-JSl-JJI

